The Mercury On-The-Go drive, from OtherWorldComputing requires no external power supply. The bus-powered hard drive has a massive 200GB of storage, which should be more than enough for your travel needs. Supported are USB 2.0, SATA, and FireWire 400 and 800.
The price on this is a bit steep, at US$379.99, but you are paying for all those gigabytes of storage. The bare-bones 120GB version is just USB and will run you US$149.99. The mid-range option adds FireWire capabilities and a corresponding $130 to the price tag.